This application claims priority upon German application 198 49 457.2 filed Oct. 28, 1998, which is incorporated herein by reference.
The invention relates to a universal joint with a first joint yoke and a second joint yoke. The yokes are connected to one another by a cross member with a bearing bush and intermediate rolling contact members. Thus, the yokes articulate around two axes. The two joint yokes each include two yoke arms. Bearing bores extend through the yoke arms to accommodate the bearing bushes of the cross member so that they are centered on one axis. These universal joints frequently form part of propeller shafts which include two such universal joints connected to one another by a connecting shaft. Attaching mechanisms are included at the ends to connect with a driving component and driven component, respectively. Such propeller shafts are used in motor vehicles, for example, in the driveline of a motor vehicle, of a commercial vehicle or, for example, in the field of engineering. If they are used in a motor vehicle, flange connections are included for attachment purposes. A first flange is attached to one of the universal joint. The first flange may be connected by a matching flange secured to a gearbox output journal. A second flange may be arranged on an input journal of a further drive, such as the axle drive. The propeller shaft or a driveline composed of several such propeller shafts serves to transmit torque, starting from the driving unit, via the gearbox, to the axle drive. Since the installation space is narrow and the flange connection is difficult to handle, the connection is complicated and expensive. Furthermore, the flanges require a great deal of machining work. Also, due to the high torque values, the flanges are provided with flange faces which engage one another. Further, in the case of heavy propeller shafts, due to the diameter conditions, it is not possible to thread, for assembly purposes, the cross member onto a joint yoke with closed bearing bores. This is the reason why, in the case of such universal joints, the yoke arms are divided, and the bridge members, like the corresponding faces of the yoke arms, have swallow tail guides, for example, to achieve positive form-fitting conditions. Machining such form-fitting connections is expensive. Due to high production costs, this is the reason why the application of such embodiments is limited to driveshafts for particularly high torque values like those that occur in rolling mills.
It is an object of the present invention to provide a universal joint which can be easily assembled or assembled onto a driveshaft.
In accordance with the invention, a universal joint has a first joint yoke. The first joint yoke includes a first base portion and two first yoke arms which project from the base portion. Each first yoke arm is provided with a first bearing bore. The two first bearing bores are arranged on a common first bore axis, as well as a first longitudinal axis intersecting the first bore axis at a right angle. A second joint yoke is made of steel and includes a second base portion and two second yoke arms. The second yoke arms project from the base and are each provided with a second bearing bore. The two second bearing bores are arranged on a common second bore axis, as well as a second longitudinal axis intersecting the second bore axis at a right angle. The two second yoke arms are separated in the region of their respective second bearing bore. Thus, yoke arm portions are formed which are connected to the respective second base portion. Also, a respective separate bridge portion is formed. The bridge portions and the yoke arm portions, in the region of the parting line with the fracture faces contacting one another, are connected to one another by bolts which pass through the fracture faces. The second yoke arms along the length of the second bearing bores, in each of two diametrically arranged linear regions, are subjected to such a heat treatment and/or separating speed, which leads to the fracture faces having a surface structure which corresponds to a brittle fracture. A cross member with four journals is received in the bores. Two journals are received in the first bearing bores. Rolling contact members and bearing bushes are arranged between the journals and bores. The other two journals are received in the second bearing bores. Likewise, rolling contact members and bearing bushes are arranged between the journals and bores.
An advantage of this embodiment is that with the fracture faces it is possible to achieve a close connection between the bridge portions and the yoke arm portions. This design enables the components to be associated with one another in a certain configuration due to the unique individual characteristics of the fracture faces. The fracture faces provide a tooth or meshing effect. Thus, the faces achieve a close connection in the torque transmitting direction around the longitudinal axis and require a small number of bolts. Preferably, only one bolt per pair of fracture faces. The heat treatment, in a concentrated way, results in material embrittlement in the region of the bearing bores. The heat treatment need only extend down a short distance to achieve an advantageous separation, similar to a brittle fracture. As an alternative, it is also possible to influence the condition of the fracture face by the speed of the separating operation. The heat treatment and separating speed are adapted to one another such that the surface structure, in the region of the fracture faces, corresponds to that achieved by a brittle fracture. In a preferred embodiment, steel is used which advantageously affect the brittle fracture behavior. For instance, steel with a carbon content equal to or greater than 0.38%, preferably a carbon content of 0.7% to 0.8% are used. The steel also includes small amounts of alloying elements. In an advantageous embodiment, a steel with 0.01% to 0.06% of sulfur or, optionally, 0.60% to 1.46% of manganese is used.
In the course of the production process, it is possible for the two second bearing bores of the joint yoke to be machined to their end condition prior to separation. The two second joint yokes are subjected to a force influence, starting from the two second bearing bores for separation purposes. The applied force preferably concentrates on the respective diametrically arranged linear regions of the second bearing bores. The heat treatment can be carried out by a laser beam. Suitable steels which meet the respective requirements are preferably steels of the following grades: 38MnSiVS5, 80MnS, C70S6BY, C45MnSBY and C50MnSBY. As a result of the heat treatment, martensite is formed in the treated region. This formation advantageously affects the brittle fracture behavior characteristics. Care must be taken during the separating operation to ensure that separation takes place as quickly as possible in those regions which are not subjected to heat treatment because the latter is restricted to a depth which is smaller than the material thickness in the region of the bearing bore. Quick separation is important so that there is no time for the formation of plastically deformed portions. This is important because a certain material toughness is required for torque transmitting purposes.
From the following detailed description, taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.